Many conductive layers, such as silicon, aluminum, and the like, are too reflective and cause problems, such as reflective notching, when patterning a photoresist layer that overlies the conductive layer. At short wavelengths, materials are generally more reflective, and therefore, an antireflective layer may become virtually required. Antireflective layers are used to reduce the likelihood of printing problems, such as reflective notching. Examples of antireflective layers include silicon nitride, silicon-rich silicon nitride, silicon oxynitride, titanium nitride, or the like.
As used in this specification, a reflective layer is not considered part of an antireflective layer. Silicon layers may be used as a gate electrode or local interconnect and is generally reflective. Patterning a photoresist layer over these layers typically results in reflective notching if an antireflective layer is not used.
Typically, an antireflective layer having a uniform composition is used. However, a uniform composition antireflective layer can have problems being integrated into an existing process flow. Silicon nitride does not adhere well to some refractory metal silicides. Silicon-rich silicon nitride can act as a leakage path between conductors or react with an adjacent layer or certain ambients, such as oxygen.